Method of making or repairing a getter vacuum pump



Dev:. 30, 1969 J. c. MALIAKAL.

METHOD OF MAKING GR REPAIRING A GETTER VACUUM PUMP Original Filed Aug.50, 1965 ROUGH PUMP 2s E\ VACUUI T SYSTEM mil/Zn J m I FIG. I

[ELECTROPOLISH PuMP BODY SANDBLAST PUMP BODY REMOVE GRIT ASSEMBLE PuMPusme OUTSIDE PuMP REDUCE PRESSURE IN MAIN PuMP TO IO3 TORR.

BAKE AT 500 C REDUCE PRESSURE TO :0 'TORR.

(RUN MAIN PUMP WITHOUT COOLANT) ADD COOLANT IRUN PUMP TO BLANK FIG. 2

3,486,213 METHOD OF MAKING 0R REPAIRING A GETTER VACUUM PUMP Joseph C.Maliakal, Waltharn, Mass, assignor to Norton Company, Worcester, Mass, acorporation of Massachusetts Continuation-impart of application Ser. No.702,482,

Feb. 1, 1968, which is a continuation of application Ser. No. 483,549,Aug. 30, 1965. This application Aug. 27, 1968, Ser. No. 767,022

Int. Cl. 322d 19/10 US. Cl. 29156.4 9 Claims ABSTRACT OF THE DISCLOSUREMethod of manufacturing a getter vacuum pump to avoid pump wall getterpeeling problems by running an initial pumping cycle with the pump wallheld above maximum operating temperature of normal cycling whilereceiving an initial deposit of getter material.

The present invention relates to a method of building getter ion vacuumpumps and more particularly to a method of surface finishing the body ofan orbiting electron vacuum pump (hereinafter orbitron pump).

This application is a continuation-in-part of Ser. No. 702,482 which isa continuation of Ser. No. 483,549.

Orbitron pumps and many other types of getter ion pumps were introducedto the art by R. G. Herb and colleagues at the University of Wisconsinlaboratories. These getter ion pumps have the unique advantage that theycan pump active and inert gases without the use of hydrocarbon oils, asin diffusion vacuum pumps, and without the use of magnets, as insputter-ion vacuum pumps. However, a substantial stumbling block to widecommercial use of getter ion pumps is an unfortunate tendency towardsshort useful life between maintenance cycles.

The relatively short useful life of orbitron pumps stems from the factthat these pumps, like other getter ion pumps, depend upon theevaporation of a getter material and deposition of the material on thepump wall. A film of getter material builds up and then tends to peelfrom the Wall in long strips. In order to analyze this penomenon, Ioperated an orbitron pump, then air released it and repeated thisprocedure several times. Severe peeling occurred. I examined the peeledsection under a microscope and found that the getter material (titanium)appeared in distinct striations corresponding to the number of times thepump was cycled. The striations were well bonded to each other, but theyhad separated from the pump wall indicating poor adhesion between thefirst layer of titanium and the pump wall (stainless steel).

It is therefore an object of the invention to provide a method of layingdown an adherent initial coating of getter material upon the wall of anorbitron pump to condition the wall.

In general, this is accomplished by initially operating the pump itselfin a temperature range higher than any operating temperature of thepump. Prolonged operation under this condition builds up a thin coatingof getter material over the surface of the pump wall which is adherentto the pump wall and will also be adherent to further layers of gettermaterial which will be deposited in subsequent operating cycles.

For a further description of my invention, reference should be had tothe following specification and accompanying drawings wherein:

FIG. 1 is a diagrammatic view of conventional apparatus used in thepractice of my invention; and

FIG. 2 is a chart indicating the sequence of steps.

nited States Patent 0 3,486,213 Patented Dec. 30, 1969 Referring to FIG.1, there is shown a conventional orbitron pump 10. The pump comprises abody 12. Stainless steel piping 14 is soldered to the body for the flowof coolant liquid around the body. Within the pump is a centralelectrode rod 16 mounted from a flange 20. A power supply (not shown) isconnected between the central electrode 16 and pump body 12 so that thecentral electrode becomes the anode and the body, the cathode of theelectrical pump. At least one filament 18 is mounted at the end of thepump from flange 20. The filament 18 is shielded from the anode 16 sothat, when the filament is heated, electrons are emitted with sufiicientangular momentum to enable them to go into orbit around the centralanode. The electrons tend to orbit around the anode until they collidewith a gas molecule in the pump or crash into a cylinder 22 of titanium,mounted on anode rod 16.

The positive ions, formed by electron collisions with air molecules, areattracted to the wall 12. The titanium cylinder 22 heats up under theeifect of electron bombardment and titanium vapors are emitted fromcylinder 22 and condensed on wall 12. The titanium, by physical burialand/ or chemical combination, pumps most of the air in the pump.

Bake-out heaters 24 are provided to prepare the pump for each new vacuumpumping cycle. The heaters are in the form of an electric blanketwrapped around the pumps.

In a typical arrangement, the orbitron pump 10 is connected to a vacuumsystem 26 which may be a bell jar. The vacuum system and orbitron arealso connected to a roughing pump 28 and a high vacuum pump 30 throughvalves 32 and 34, respectively. The pump 28 is typically a cryosorbtionpump or a rotary mechanical pump with a zeolite inlet trap. The pump 30may be a diffusion pump, a titanium getter pump, a cryopump, or forpurposes of the present invention, another orbitron pump.

The conventional cycling of the orbitron pump, starting from atmosphericpressure is as follows. The vacuum system and orbitron are evacuatedthrough valve 32 by operation of pump 28 until a pressure of about 10"mm. Hg (torr) is achieved. Then the pump 30 is operated to lower thepressure still further. During operation of the pump 36, the bake-outheaters 24 are run to raise the temperature of walls 12 to about 250400C. This bakeout temperature is normally the maximum temperature to whichthe orbitron is exposed in its various pumping cycles and is hereinafterreferred to as the maximum operating temperature of the pump. Initially,the bakeout causes the pressure in the orbitron pump to rise ascontaminants are driven from the wall of the orbitron at a rate fasterthan the effective pumping speed of pump 30 (taking into account theconductance of the interconnecting piping thereof). After a short period/2 to about 4 hours), the pressure decreases. Then bake-out isterminated. The power is fed to the orbitron and cooling Water isadmitted to the coils 14 and the orbitron pump is run to lower thepressure therein (and in the system) to blank-off or as low as desired.From time to time, gas may be leaked into the system through a bleedvalve (not shown). If the gas is inert, the pump-down can be repeatedwithout the bake-out step. If a full atmosphere of air is admitted tothe system, then the bake-out is generally included as part of the nextpump-down cycle.

It is the conventional operation described above that produces theproblem of titanium peeling at Wall 12. I have discovered a method ofoperating the pump as part of the manufacturing process. Following myprocess, the pump can go through several normal operating cycles, asdescribed above, and it will be seen that the peeling problem has beensubstantially eliminated.

My improvement consists of running a special pumping cycle as part ofthe manufacturing (or reconditioning) process wherein the orbitron pumpis actually operated during a special bake-out. The special bake-outinvolves heating the orbitron wall to a temperature in excess of themaximum operating temperature (e.g. heating to 500 C. as part of thespecial treatment where the maximum operating temperature is 400 C.).

A preferred embodiment of my improvement manufacturing process is nowdescribed. Reference should be made to FIG. 2, which is a chart of thesteps of the improved process according to the preferred embodiment.First, the pump body is cleaned by electropolishing technique. Thesecond step is to further clean the body by abrasive blasting. The thirdstep is to remove grit from the wall 12 of the pump body. This can bedone, for instance, by washing with alcohol. Then the pump 10 (FIG. 1)is assembled by welding its parts together or brazing with or withoutvacuum and bycapping with the flange 20, using a demountable seal suchas a metal gasket. The pump inlet is connected to a vacuum system 26(which may be no more than a gauge and a bleeder valve) and to the pumpsand valves 2834 as shown in FIG. 1. The pump 28 is then operated (stepfive) to reduce the pressure in the system to 10- torr (corresponding toabout 10 torr in the pump 10 itself). Step six comprises operation ofthe bake-out heaters 24 to heat the wall to 500 C. This heating iscontinued for at least 3 hours. The pump 30 is operated throughout stepsix and in most cases, it will be observed that the pressure falls to 10torr. If the pressure fails to reach 10- torr (e.g. because of a lowspeed pump 30) step six should be continued beyond three hours until 10torr or below is attained. During step six, it is advisable to blow airacross flange 20 to cool the demountable seal. A small electric fan issufficient for this purpose. Step seven comprises turning on theorbitron pump 10 and running it at 500 C. This causes a thin initiallayer of titanium (a few monolayers) to deposit on the wall. Thisrunning of the orbitron pump without the use of coolant also reducespressure to l torr. Once stable operation of the orbitron is achieved,the pump 30 can be cut off. The orbitron is run hot until it pulls thepressure down to torr. The reduction of pressure by a full decade inthis range indicates that titanium is starting to adhere to the wall 12of the orbitron. Operation of the orbitron under heat should becontinued for 23 hours after 10- torr or better is achieved. Then thebake-out is terminated by cutting off heaters 24 and admitting coolingwater to coils 14 very slowly (step eight). Step nine comprisesoperating the pump until blank-off is achieved. After this, the pump 10can be turned 01f and air released and is then ready for normaloperating cycles as described earlier.

The net result of my improved manufacturing process is that a veryadherent primer coat of titanium is formed on the pump wall 12. Sincethis coat is formed at temperatures in excess of the maximum operatingtemperature of the pump, the prime coat will not be caused to strip orpeel by any conditions occurring in the normal operating cycle.Cleanliness is essential to the formation of a good primer coat and thisis achieved by applying the primer coat at a pressure on the order of10- or 10 torr, a pressure range which is practical for the orbitron toachieve at treatment temperatures on the order of 500 C.

The choice of treatment temperature is preferably at least 100 C. abovethe maximum operating temperature of the pump. Thus, if it is necessaryto bake-out the pump at 350 C. maximum during a normal operating cycle,the treatment temperature used in steps six and seven of mymanufacturing process should be at least 450 C. If a step seven at lowertemperature is necessary to reach 10- torr, the step seven should becarried out at no lower than about 375 C.

The pumps 28 and 30 can be combined into a single pump if a molecularpump or cryosorption pump is used. If a mechanical pump 28 or adiifusion pump 30 are used, in-line trapping should be provided toprevent hydrocarbon vapors from reaching orbitron 10 during themanufacturing process.

The method of the invention has been particularly described in itsapplication to getter ion vacuum pumps 01' the orbitron type. It shouldbe noted that the method is similarly applicable to other forms ofgetter ion vacuum pumps and to heated getter source vacuum pumps whichoperate without any ionization of gasses within the pump. such as thegetter pumps which include resistance heated getter cartridge sources.

Since several variations can be made within the scope of my invention,it is intended that the above description and accompanying drawingsshall be read as illustrative and not in a limiting sense.

What is claimed is:

1. An improved method of manufacturing a getter vacuum pump comprisingthe steps of cleaning the pump body, assembling the pump and connectingit to outside pumping means, operating said outside pumping means toreduce the pressure within the getter pump to about 10 torr, heating thegetter pump body during the latter portion of the above said pressurereduction at a temperature in excess of the maximum operatingtemperature of the getter pump body, then operating the getter pumpwhereby a getter source in the pump is heated to emit getter materialtherefrom while the pump body is at said elevated temperature to reducepressure therein whereby an adherent primer coat of getter material isestablished on the inner wall of the getter vacuum pump body.

2. The method of claim 1 wherein said elevated temperature is about 5 00C.

3. The method of claim 1 wherein said pump is a getter ion pump.

4. The method of claim 2 wherein said pump is of the orbitron type.

5. An improved method of manufacturing or repairing a getter vacuumpump, of the type whose structure and normal operations include meansfor and the step or heating a getter source in the pump to emit gettermaterial therefrom and condensing it on a wall of the pump, comprisingthe steps of cleaning said pump wall, assembling the pump and connectingit to an outside pumping means, operating said outside pumping meanspump wall at about 500 C. during the latter portion of said pressurereduction step, said vacuum level being selected to be at a pressure nohigher than about 10*" torr and being achieved after an initial pressurerise due to commencement of said pump wall heating step and then heatingsaid getter source to emit getter material therefrom to further reducepressure in the pump while continuing said heating of the pump wallwhereby an adherent primer coat of getter material is established onsaid wall.

6. An improved method of manufacturing or repairing a getter vacuumpump, of the type whose structure and normal operation includes meansfor and the step of heating a getter source in the pump to emit gettermaterial therefrom and condensing it on a wall of the pump and alsoincludes means for and the step of bake-out of the pump wall from timeto time comprising the steps of cleaning said pump wall, assembling thepump and connecting it to an outside pumping means, operating saidoutside pumping means to reduce the pressure in the pump to a vacuumlevel, heating the pump wall at an elevated temperature during thelatter portion of said pressure reduction step, said vaculm level beingselected to be at a pressure no higher than about 10- torr and beingachieved after an initial pressure rise due to commencement of said wallheating step to further reduce pressure in the pump while continuingsaid heating of the pump wall whereby an adherent primer coat of gettermaterial is established on said wall.

7. The method of claim 6 wherein said elevated temperature is at leastC. higher than bake-out temperature.

5 8. The method of claim 6 wherein said elevated Wall 1,971,433temperature is about 500 C. 2,668,253 9. The method of any of claims 1-3wherein said 2,993,638 further reduction of pressure by operating thepump is at 3,149,774

least a decade (power of ten of mm. Hg pressure drop).

References Cited Tartrais 29-1564 Taylor 117221 Hall et a1. 313-73Jepsen 3137.3

5 JOHN F' CAMPBELL, Primary Examiner R. J. CRAIG, Assistant ExaminerUNITED STATES PATENTS 9/1912 Gage 29-1564 1/1927 Thomas et al. 29l56.410 29-401 US. Cl. X.R.

